skip to main content

Trimethoprim Creatinine Interference — ESENeph MCQ

Instant feedback + full explanation. One question, done properly.

EasyAcute Kidney InjuryTrimethoprim Creatinine InterferenceESENeph

A 50-year-old man with an eGFR of 42 mL/min/1.73m2 is prescribed Trimethoprim for a UTI. After 5 days, his creatinine rises from 140 to 185 umol/L. He is well, with no signs of sepsis or obstruction. What is the most likely explanation?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Trimethoprim inhibits tubular creatinine secretion, causing a rise in serum creatinine without true GFR change

Trimethoprim competitively inhibits the organic cation transporter in the proximal tubule responsible for creatinine secretion. This causes a reversible rise in serum creatinine (typically 20-40 umol/L) without any actual change in true GFR. This is a pharmacological effect, not nephrotoxicity. The rise occurs within days and reverses on stopping the drug. Clinicians should be aware of this to avoid unnecessary investigations or treatment changes. True Trimethoprim nephrotoxicity (hyperkalaemia via ENaC blockade) is a separate concern.

Reference: KDIGO 2024 – CKD; Delanaye et al 2011 – Creatinine Interference Review